Well, you said it yourself. The mains are huge! Although since the naturals are pretty squished in there it isn't all that bad. honestly though I think the biggest problem is grabbing a 3rd. You either take the base in the middle of the map, which is going to be just about impossible to hold because of how open it is, plus it's harass-able by air from the behind. So, if you can't take that you then have to expand 1/2 way up the map to grab the bases on the edges. But that only has 1 gas?
You shouldn't put 4 minerals on each side, because it can mess with the worker AI. They won't migrate from one side of the minerals to the other side, they'll mine out the 4 then sit there, which could be a problem. Although I guess it'd require more APM to make sure your workers are mining correctly but still it's usually better to put them all together.
Unsure if all positions are available or if it's cross only? But since grabbing a 3rd is almost impossible anyway I don't think it really matters that much.
Are there any xel'naga watch towers? I can't see any. might be a good idea to add one or two since it's a 4player map. Even just one in the middle is better then none (although a lot of people might tell you otherwise).
If you're going to make a map thread you should try a little harder on the format.
Bold some things, add more pictures, underline things, give us more information about it. The number of bases, the number of watchtowers, the nat 2 nat rush distance, which region it's uploaded too, etc etc etc.
Aesthetics aren't too bad, except the edges of the map are quite bare. Although it's also pretty hard to tell without seeing some actual close up pictures!